In the process for manufacturing aluminium, after completion of the refining process, the molten aluminium is cast into ingots or billets that are subsequently used in processes for manufacturing aluminium products, for example aluminium foil.
During the casting operation, the molten aluminium is transferred from a holding furnace into a water-cooled mould above a casting pit, where it solidifies to form an aluminium ingot.
It is important that the flow of aluminium into the mould is smooth and non-turbulent, so that the solidification and temperature profile of the metal can be carefully controlled. If the flow is turbulent, impurities can be introduced into the aluminium, which can cause serious problems during subsequent manufacturing processes.
To avoid turbulence and to optimise distribution, the molten aluminium is usually poured into the mould through a distributor device. Conventionally, this consists of a flexible bag of coated woven glass fibres, known as a “combo bag”, having an outer shell of solid woven fabric with normally two large openings through which the molten aluminium flows, and an inner liner of open-weave fabric. In use, the molten aluminium flows through the small pores of the open-weave liner, then through the openings in the outer shell, which helps to prevent turbulence in the flow of aluminium.
Conventional distributor devices can be used only once and are then discarded. However, because these devices are constructed largely by hand, they are relatively expensive and their use therefore adds significantly to the cost of the manufacturing process.
Conventional distributor devices are normally quite flexible, or at best semi-rigid. This means that the positioning and shape of the device can be inconsistent, and the dimensional accuracy of the device is difficult to measure and control within normal engineering tolerances. Furthermore, the coatings on the woven glass fibre weaken at metal casting temperatures, leading to reduced rigidity of the distributor. These factors combine to limit the reliability of metal distribution, and this leads to inconsistencies in the casting operation.
Further, fibres can occasionally come loose from the fabric of the distributor and become entrained in the molten aluminium, thereby introducing impurities into the aluminium ingot and potentially causing considerable difficulties in subsequent manufacturing processes.
Further, conventional distributors do not drain well after use and are sometimes provided with additional drain apertures in the bottom wall of the outer shell to ensure complete drainage. However, aluminium can also flow through these apertures during casting, thereby disturbing the desired liquid metal flow pattern.
Another distributor device described in U.S. Pat. No. 5,207,974 has a “bag-in-bag” design, comprising an inner bag of impermeable fabric and an outer bag having outlet openings. The device is suspended above the mould and liquid metal is poured into the inner bag. When the metal reached the top of the inner bag, it overflows into the outer bag, then flows through the openings into the mould. The bag is flexible and is susceptible to the disadvantages mentioned above.
U.S. Pat. No. 5,871,660 describes two different distributor devices. One of these is a flexible bag type, which is susceptible to the disadvantages mentioned above. The other device comprises a rigid nozzle having four outlet openings that are angled to direct the molten metal towards the sides of the mould. The nozzle is geometrically complex and is difficult and expensive to produce.